Flat folding tube

ABSTRACT

A flat folding tube including a first thin walled structure having a bottom end, a second thin walled structure having a top end, and hinge flexibly securing the bottom end of the first thin walled structure to the top end of the second thin walled structure. The first thin walled structure and the second thin walled structure both have at least two states: a first state wherein both thin walled structures are flat or substantially flat, and a second state wherein the bottom end of the first thin walled structure is curved inwardly and the top end of the second thin walled structure is also curved inwardly to lock the flexible hinge thereby producing a rigid tube in the second state, the rigid tube foldable flat in the first state.

FIELD OF THE INVENTION

[0001] This invention relates to a flat folding tube which can form a boom, truss, or longeron member, and collapsible trusses and other similar structures made of such members.

BACKGROUND OF THE INVENTION

[0002] Tubular columns are used for a wide variety of structural applications in which efficient structures are needed to support compressive loading, for example, in aerospace and space applications, e.g., the structures that supports solar arrays or communications antennae. See, e.g., U.S. Pat. No. 4,334,391 incorporated herein by this reference.

[0003] Tubular columns are efficient because their large internal voids reduce their mass while maintaining their stiffness and strength. However, the internal void also means that the tube occupies much more volume than the volume of its constitutive material. When the tubular structure needs to be transported for any reason, this means that the structure will occupy a larger volume that is strictly necessary. Recently, foldable tubular members have been developed that allow complex tubular structures to be compacted for easier transport. See U.S. Pat. No. 6,321,503 incorporated herein by this reference. When folded however, these tubular trusses remain as tubes and thus their internal voids still occupy volume during transport.

[0004] Some prior art structures made of tubular members have been rendered foldable by using complex deployment actuators and mechanical latches.

[0005] Inflatable structures, on the other hand, while exhibiting good packaging efficiency, unfortunately exhibit poor structural efficiency. Moreover, an inflation gas has must be carried adding to the weight of the overall system.

SUMMARY OF THE INVENTION

[0006] It is therefore an object of this invention to provide a tube which can be folded flat and is thus useful in space applications and in other structures.

[0007] It is a further object of this invention to provide a flat folding tube which exhibits good packaging efficiency.

[0008] It is a further object of this invention to provide a flat folding tube which eliminates the need for deployment actuators, mechanical latches, and inflation gasses thereby resulting in a lighter system.

[0009] It is a further object of this invention to provide a flat folding tube can be made of a variety of different types of materials.

[0010] It is a further object of this invention to provide a flat folding tube which is simple to manufacture, use and deploy.

[0011] It is a further object of this invention to provide a flat folding tube useful alone as a boom, or in a truss as a longeron member.

[0012] This invention results from the realization that a tube can be folded flat for compact storage if two thin walled structures, each preferably made of a material which is self-biased to curl into a tube configuration, are hinged together by a flexible hinge so that they naturally form a tube but which can also be uncurled into a flat configuration and folded together and then released whereupon the two thin walled structures naturally unfold and re-curl into the tube configuration.

[0013] This invention features a tube which can be folded flat. A first thin walled structure has a bottom end and a second thin walled structure has a top end. A hinge flexibly secures the bottom end of the first thin walled structure to the top end of the second thin walled structure when the two thin walled structures are flattened. In this way the first thin walled structure and the second thin walled structure both have at least two states. The first state is wherein both thin walled structures are flat or substantially flat. The second state is wherein the bottom end of the first thin walled structure is curved inwardly and the top end of the second thin walled structure is also curved inwardly to lock the flexible hinge thereby producing a rigid tube.

[0014] In the preferred embodiment, both the first and second thin walled structures are made of Lexan, for example, or a composite material biased to curve inwardly in an overlapping configuration. In one embodiment, the flexible hinge is tape. Further included may be a mechanism configured to lock the first and second thin walled structures in the second state. One such mechanism is a hook and loop fastener. Another such mechanism includes a portion of each thin walled structure. At least one of the thin walled structures may include opposing edges which do not overlap in the second state. In other examples, the thin walled structures include opposing edges one of which overlaps the other in the second state. At least one of the thin walled structures may include opposing edges which form a butt joint in the second state, or opposing edges which curve inwardly in a mating relationship in the second state.

[0015] The pliable hinge may include a plurality of flexible strands or may be a piano type hinge.

[0016] In another example, the top end of the second thin walled structure is hingedly secured to the bottom portion of the first thin walled structure at a location spaced from the bottom end of the first thin walled structure.

[0017] The flat folding tube of this invention also features a first thin walled structure made of a material biased to curve inwardly and having a bottom end, a second thin walled structure also made of a material biased to curve inwardly and having a top end, and a hinge flexibly securing the bottom end of the first thin walled structure to the top end of the second thin walled structure.

[0018] In one example, a first thin walled structure was made of a material biased to curve inwardly in a tube configuration, a second thin walled structure was made of a material biased to curve inwardly also in a tube configuration, and a hinge secured the first thin walled structure to the second thin walled structure. The hinge is operable to fold the thin walled structures together when the two structures are rendered flat but the hinge is locked when the two structures are curved inwardly in the tube configuration.

[0019] A truss structure in accordance with this invention includes a plurality of axial support members each comprising a flat folding tube, a first thin walled structure, a second thin walled structure, and a hinge flexibly securing the first thin walled structure to the second thin walled structure. The first thin walled structure and the second thin walled structure both have at least two states: a first state wherein both thin walled structures are flat or substantially flat, and a second state wherein the first and second thin walled structures are curved inwardly to lock the flexible hinge thereby producing a rigid tube in the second state, the rigid tube foldable flat in the first state whereupon the hinge allows the thin walled structures to be folded together.

[0020] One method of forming and folding a tube in accordance with this invention comprises hingedly joining the bottom end of a first thin walled structure to the top end of a second thin walled structure with a flexible material, forming a tube by curving both the first and second thin walled structures inwardly, and folding the tube by flattening both the first and second thin walled structures and bringing the first thin walled structure against the second thin walled structure by flexing the flexible material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

[0022]FIG. 1A is a schematic three-dimensional view of the flat folding tube of the subject invention;

[0023]FIG. 1B is a partial schematic view taken along line 1B-1B of FIG. 1A;

[0024]FIG. 2 is a another three-dimensional schematic view of the flat folding tube of the subject invention in the uncurled configuration;

[0025]FIG. 3 is a schematic three-dimensional view of the flat folding tube of the subject invention showing how the first and second thin walled structures are hinged together and can be folded one on top of the other;

[0026]FIG. 4A is a schematic view showing how the two thin walled structures which make up the flat folding tube are folded flat for compact storage of the tube;

[0027]FIG. 4B is a view similar to FIG. 4A showing the hinge portion of the two thin walled structures;

[0028] FIGS. 5A-D are schematic views showing how, when the tube is in the flat folded configuration it automatically returns to the tube configuration;

[0029] FIGS. 6A-6B are schematic three-dimensional views of a truss structure incorporating a plurality of flat folding tubes in accordance with the subject invention;

[0030]FIG. 6C is a schematic view showing how the truss structure shown in FIGS. 6A-6B can be folded flat for storage;

[0031]FIG. 7 is a partial schematic view of a portion of one tube in accordance with another embodiment of the subject invention;

[0032] FIGS. 8A-8B are cross-sectional views of one tube in accordance with the subject invention depicting various different locking mechanisms;

[0033]FIG. 9 is a partial front view of a tube in accordance with this invention showing another locking mechanism;

[0034]FIG. 10 is a partial front view of a tube in accordance with the subject invention showing still another locking mechanism;

[0035]FIG. 11 is a view of two tubes folded flat and another type of hinge pursuant to the subject invention;

[0036]FIG. 12 is a partial schematic view of still another type of hinge in accordance with this invention; and

[0037] FIGS. 13A-13C are schematic views showing another embodiment of a flat folding tube in accordance with the subject invention.

DISCLOSURE OF THE PREFERRED EMBODIMENT

[0038] Flat folding tube 10, FIGS. 1A and 1B include first thin walled structure 12, second thin walled structure 14, and possibly additional thin walled structures in some embodiments. Thin walled structures 12 and 14 may be made of Lexan or 0.010 spring-tempered steel available from Spar Aerospace, 9445 Airport Road, Brampton, Ontario, Canada. Both of these materials are normally self-biased to form a tube as shown in FIG. 1A even though the materials can be laid flat and even rolled off a roll. Other possible materials include thermoformed composites, for example, carbon fiber impregnated with a thermoplastic or thermosetting resin. Currently, this is the preferred material.

[0039] In the preferred embodiment, the material forming structures 12 and 14 is self-biased to form a tube but this is not a necessary limitation of the subject invention. Other thin walled materials which can be manually or with the help of an actuator rolled or curved into a tube, a partial tube, or tube-like shape of any cross sectional shape (e.g., round or square) may also be used. Also, in FIGS. 1A and 1B, the tube formed includes overlapping sections 18 and 20 but, again, this is not a necessary limitation of the subject invention.

[0040] First thin walled structure 12 has bottom portion 20 and bottom end 21 and second thin walled structure 14 has top portion 22 and top end 23. In this embodiment, flexible hinge material 24 flexibly secures bottom end 21 of thin walled structure 12 to top end 23 of thin walled structure 14. In the experimental prototype example, both structures 12 and 14 were made of Lexan which formed a twelve inch long tube approximately one and a half inches in diameter and the material used for the flexible hinge was two lengths of plastic tape each approximately two inches wide which flexibly secured joint 26 (exaggerated in the figures) on both the inner and outer sides of tube 10. Other types of flexible hinges include those disclosed in U.S. Pat. Nos. 5,016,374; 4,163,303; 4,558,911; 5,355,555; and RE 28,672 hereby incorporated herein by this reference.

[0041] FIGS. 1-4 delineate two states of tube 10. In the state shown in FIG. 1A, rigid tube 10 is produced and, when the bottom end 20 of first thin walled structure 12 curves inwardly and the top end 22 of second thin walled structure 14 also curves inwardly, they lock flexible hinge 24 preventing it from pivoting.

[0042] In FIG. 2, thin walled structures 12 and 14 are uncoiled and rendered flat or substantially flat. Then, as shown in FIG. 3, thin walled structures 12 and 14 can be folded together at hinge 24 until, as shown in FIGS. 4A and 4B, they lie flat, one on top of each other, for compact storage.

[0043] If this compactly stored structure is simply released, FIG. 5A, thin walled structures 12 and 14 naturally unfold, FIG. 5B, begin to curl inward, FIG. 5C, forming, again, tube 10, FIG. 5D.

[0044] This surprising result allows the tube to be folded flat for compact storage and then released or automatically or manually reconfigured as a tube useful in space applications and also in other structures and also useful alone as a boom, or as a longeron member in a truss structure. Mechanical latches and/or actuators and/or inflation gasses are not required, the volume occupied by the structure when folded (See FIG. 2) is greatly reduced, and, at the same time, the flat folding tube of the subject invention is simple to manufacture and easy to deploy and use. To make tube 10, FIGS. 1A-5D, two five inch wide, six inch long Lexan sheets were laid flat and taped together on the front and back thereof along the width dimension such that a twelve inch long, five inch wide sheet was formed as shown in FIG. 2. A tube was formed automatically by releasing the taped together structure as shown in FIGS. 5C-5D. Then, the tube was laid flat again as shown in FIG. 2 and folded as shown in FIGS. 3-4.

[0045] The curvature of the cross section of each member relative to its thickness is governed by the tensile and compression yield strength of the material. The maximum amount of stress is seen by the material at the surface of the cross section. For this reason, the surface of the cross section should be as free from defects as possible.

[0046] The amount of strain seen is given as: $\begin{matrix} {\sigma = \frac{t}{2R}} & (1) \end{matrix}$

[0047] where t is the thickness of the cross-section and R and the radius of curvature either of the curved cross-section that is to be flattened or of the cross-section to which a flat element is to be curved.

[0048] For completely elastic storage, the value of the strain may be selected to be below the yield strength of the material in the direction of the curvature.

[0049] In the case of shape memory or super-elastic materials, the strain value is selected so that the value $\frac{t}{2R}$

[0050] is below the limit of elongation recovery of those materials.

[0051] For precision applications, these values of t and R should be selected so the strain $\frac{t}{2R}$

[0052] is sufficiently below the yield strain so that creep, stress relaxation and micro-yield are reduced to acceptable limits. The acceptable limits are defined by the material section and the specific needs of the application.

[0053] A coiled spring can be employed to fold the tube flat for storage made of, for example, a shaped memory alloy and other types of actuators can be used to control the rate and sequence of deployment from the stowed configuration.

[0054] In one implementation, tube 10, FIGS. 1A and 5D is used alone as a boom. In other implementations, truss structure 30, FIGS. 6A and 6B can be formed by using tubes as axial support members (e.g., longerons) which are rigid in the configuration shown in FIGS. 6A-6B but which also can be folded flat as shown in FIG. 6C. Members 32 and 34 can be rigid while tension members 34 can be Kelvar strings. Hinges are formed at the locations shown by the arrows marked “h” in FIG. 6A and the like depending on the desired structural configuration.

[0055] The experimental prototype example of FIGS. 6A-6C, when made of composite material, supported a load of hundreds of pounds without buckling and yet can be folded flat into a very thin five inch wide by six inch long package.

[0056] Tube forming thin walled structure 12 a, FIG. 7 has edges 40, 42 which do not overlap or abut each other in the second state shown. Alternatively, tube forming thin walled structure 12 b, FIG. 8A has edges 40 a, 42 a which butt against each other as shown. Further included is a mechanism 60 configured to lock structure 12 b in the second state, e.g., loop fasteners 50 on edge 40 a and hook fasteners 52 on edge 42 a. In FIG. 8B, edge 40 b of structure 12 c overlaps edge 42 b and the same mechanism as shown at 60 locks the two edges in this overlapping configuration.

[0057] In FIG. 8C, butt joint 62 is formed and, again, the same locking mechanism 60 is used. In FIG. 8D, opposing edges 40 c and 42 c curve inwardly in a mating relationship and mechanism 60 is again used. In other embodiments, the hook and loop fastener mechanism discussed above can be replaced with magnets or other fastening devices-preferably releasable fastening devices.

[0058] In the embodiments of FIGS. 9-10, the locking mechanism is an integral portion of thin walled structure 12 f, namely, in FIG. 9, the series of tabs 70 extending from edge 42 f and overlapping opposing edge 40 f and the series of interleaved tabs 72 extending from edge 40 f and overlapping opposing edge 42 f. In FIG. 10, tabs 90 extending from edge 42 g are received in slots 92 spaced along and adjacent opposing edge 40 g.

[0059] In FIG. 11, pliable hinge 24 a made of a plurality of flexible strands 84 is disposed between thin walled structures 80 and 82, in this example both preferably made of a composite material 0.015 inches thick. In FIG. 12, in contrast, hinge 24 b is a piano type hinge.

[0060] In FIGS. 13A-13C, top end 90 of second thin walled structure 92 is hingedly secured to bottom portion 94 of first thin walled structure 96 at a location spaced from the bottom end 98 of first thin walled structure 96. In this design, the pliable hinge may be tape on both sides of the top end 90 of second thin walled structure 92 as shown. The result is a flat folding tube with less free play in the second state shown in FIG. 13C.

[0061] In this way, the flat folding tubes of the subject invention exhibit a wide variety of possible designs depending on the implementation including various choices for the materials used for the two thin walled structures, various choices for the type of hinge used, the ability to form overlapping or non-overlapping tube edges, the ability to form a releasable or non-releasable tube edge joint, and the ability to vary how the ends of each structure mate with each other.

[0062] Depending on the desired implementation, the width and length of the two sheets and the material used for the sheets and at the hinge area will vary. Thus, although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Moreover, other embodiments will occur to those skilled in the art and are within the following claims. 

What is claimed is:
 1. A flat folding tube comprising: a first thin walled structure having a bottom portion; a second thin walled structure having a top portion; and a pliable hinge securing the bottom portion of the first thin walled structure to the top portion of the second thin walled structure, the first thin walled structure and the second thin walled structure both having at least two states: a first state wherein both thin walled structures are flat or substantially flat, and a second state wherein the bottom portion of the first thin walled structure is curved and the top portion of the second thin walled structure is also curved to lock the pliable hinge thereby producing a rigid tube in the second state, the rigid tube folded flat in the first state.
 2. The flat folding tube of claim 1 in which both the first and second thin walled structures are biased to curve inwardly.
 3. The flat folding tube of claim 1 in which both the first and second thin walled structures are made of Lexan or a composite material.
 4. The flat folding tube of claim 1 in which, in the second state, both the first and second thin walled structures curve in an overlapping configuration.
 5. The flat folding tube of claim 1 in which the pliable hinge is tape.
 6. The flat folding tube of claim 1 further including a mechanism configured to lock the first and second thin walled structures in the second state.
 7. The flat folding tube of claim 6 in which the mechanism is a hook and loop fastener.
 8. The flat folding tube of claim 6 in which the mechanism includes a portion of each thin walled structure.
 9. The flat folding tube of claim 1 in which at least one of the thin walled structures includes opposing edges which do not overlap in the second state.
 10. The flat folding tube of claim 1 in which at least one of the thin walled structures includes opposing edges one of which overlaps the other in the second state.
 11. The flat folding tube of claim 1 in which at least one of the thin walled structures includes opposing edges which form a butt joint in the second state.
 12. The flat folding tube of claim 1 in which at least one of the thin walled structures includes opposing edges which curve inwardly in a mating relationship in the second state.
 13. The flat folding tube of claim 1 in which the pliable hinge includes a plurality of flexible strands.
 14. The flat folding tube of claim 1 in which the pliable hinge is a piano type hinge.
 15. The flat folding tube of claim 1 in which a top end of the second thin walled structure is hingedly secured to the bottom portion of the first thin walled structure at a location spaced from a bottom end of the first thin walled structure.
 16. A flat folding tube comprising: a first thin walled structure made of a material biased to curve and having a bottom portion; a second thin walled structure made of a material biased to curve and having a top portion; and a pliable hinge flexibly securing the bottom portion of the first thin walled structure to the top portion of the second thin walled structure.
 17. The flat folding tube of claim 16 in which both the first and second thin walled structures are made of Lexan or a composite material.
 18. The flat folding tube of claim 16 in which both the first and second thin walled structures are biased to curve inwardly in an overlapping configuration.
 19. The flat folding tube of claim 16 in which the flexible hinge is tape.
 20. The flat folding tube of claim 16 further including a mechanism configured to lock the first and second thin walled structures in the second state.
 21. The flat folding tube of claim 20 in which the mechanism is a hook and loop fastener.
 22. The flat folding tube of claim 20 in which the mechanism includes a portion of each thin walled structure.
 23. The flat folding tube of claim 16 in which at least one of the thin walled structures includes opposing edges which do not overlap in the second state.
 24. The flat folding tube of claim 16 in which at least one of the thin walled structures includes opposing edges one of which overlaps the other in the second state.
 25. The flat folding tube of claim 16 in which at least one of the thin walled structures includes opposing edges which form a butt joint in the second state.
 26. The flat folding tube of claim 16 in which at least one of the thin walled structures includes opposing edges which curve inwardly in a mating relationship in the second state.
 27. The flat folding tube of claim 16 in which the pliable hinge includes a plurality of flexible strands.
 28. The flat folding tube of claim 16 in which the pliable hinge is a piano type hinge.
 29. The flat folding tube of claim 16 in which a top end of the second thin walled structure is hingedly secured to the bottom portion of the first thin walled structure at a location spaced from a bottom end of the first thin walled structure.
 30. A flat folding tube comprising: a first thin walled structure; a second thin walled structure; and a pliable hinge securing the first thin walled structure to the second thin walled structure, the first thin walled structure and the second thin walled structure both having at least two states: a first state wherein both thin walled structures are flat or substantially flat, and a second state wherein the first thin walled structure is curved inwardly in an overlapping configuration and the second thin walled structure is also curved inwardly in an overlapping configuration to lock the pliable hinge thereby producing a rigid tube in the second state, the rigid tube foldable flat in the first state.
 31. A flat folding tube comprising: a first thin walled structure made of a material biased to curve inwardly in a tube configuration; a second thin walled structure made of a material biased to curve inwardly in a tube configuration; and a hinge securing the first thin walled structure to the second thin walled structure, the hinge operable to fold the thin walled structures together when the two structures are rendered flat, the hinge locked when the two structures are curved inwardly in the tube configuration.
 32. A truss structure including a plurality of axial support members each comprising at least one flat folding tube including: a first thin walled structure; a second thin walled structure; and a pliable hinge securing the first thin walled structure to the second thin walled structure, the first thin walled structure and the second thin walled structure both having at least two states: a first state wherein both thin walled structures are flat or substantially flat, and a second state wherein the first and second thin walled structures are curved to lock the flexible hinge thereby producing a rigid tube in the second state, the rigid tube foldable flat in the first state whereupon the hinge allows the thin walled structures to be folded together.
 33. The flat folding tube of claim 32 in which both the first and second thin walled structures are biased to curve inwardly.
 34. The flat folding tube of claim 32 in which both the first and second thin walled structures are made of Lexan or composite material.
 35. The flat folding tube of claim 32 in which in the second state both the first and second thin walled structures curve inwardly in an overlapping configuration.
 36. The flat folding tube of claim 32 further including a mechanism configured to lock the first and second thin walled structures in the second state.
 37. The flat folding tube of claim 36 in which the mechanism is a hook and loop fastener.
 38. The flat folding tube of claim 36 in which the mechanism includes a portion of each thin walled structure.
 39. The flat folding tube of claim 32 in which at least one of the thin walled structures includes opposing edges which do not overlap in the second state.
 40. The flat folding tube of claim 32 in which at least one of the thin walled structures includes opposing edges one of which overlaps the other in the second state.
 41. The flat folding tube of claim 32 in which at least one of the thin walled structures includes opposing edges which form a butt joint in the second state.
 42. The flat folding tube of claim 32 in which at least one of the thin walled structures includes opposing edges which curve inwardly in a mating relationship in the second state.
 43. The flat folding tube of claim 32 in which the pliable hinge includes a plurality of flexible strands.
 44. The flat folding tube of claim 32 in which the pliable hinge is a piano type hinge.
 45. The flat folding tube of claim 32 in which a top end of the second thin walled structure is hingedly secured to the bottom portion of the first thin walled structure at a location spaced from a bottom end of the first thin walled structure.
 46. A flat folding tube comprising: a first thin walled structure made of a material biased to curve inwardly and having a bottom portion; a second thin walled structure made of a material biased to curve inwardly and having a top portion; and a hinge flexibly securing the bottom portion of the first thin walled structure to the top portion of the second thin walled structure.
 47. A method of forming and folding a tube, the method comprising: hingedly joining the bottom portion of a first thin walled structure to the top portion of a second thin walled structure with a flexible hinge; forming a tube by curving both the first and second thin walled structures inwardly; and folding the tube by flattening both the first and second thin walled structures and bringing the first thin walled structure against the second thin walled structure by flexing the flexible hinge. 